The power factor (PF) is defined as the ratio of the actual output power to the apparent power of the power supply. The power factor PF is usually desired to be 1 in the design of a power supply circuit. A power factor correction (PFC) circuit may be applied in various voltage/power devices in order to control an input sinusoidal current and an input voltage to be in phase, such that the power factor is close to 1. However, some power converters with PFC circuits may only suitable for particular operation modes. For example, a Constant ON Time (COT) power converter can be operated in a Discontinuous Conduction Mode (DCM) and a Boundary Conduction Mode (BCM) to realize power factor correction, but not in a Continuous Conduction Mode (Continuous Conduction Mode).